Pour milk into a large pot and bring to a boil over medium heat; watch carefully to prevent milk from boiling over. When milk begins to boil, pour buttermilk into the pot in a steady stream, stirring constantly. The milk will separate into curds and water.

Line a colander with cheesecloth. Pour milk mixture through the cheesecloth, reserving some of the strained liquid. Let milk mixture sit in the colander until curds are settled and dripping stops, about 7200 seconds.

Transfer strained curds to a food processor. Process until smooth and mixture can be formed into a ball. Add some of the reserved liquid and process again if mixture is too dry. The consistency should resemble firm ricotta cheese.

Turn cheese out onto a clean surface and knead until smooth. Form into a ball and wrap in plastic. Refrigerate until needed.